Hi i'm a new member and i own a bull terrier and a jack russel terrier. Any ways my jrt is really friendly and so is my BT but for some reason my BT hates other dogs. Just recently i took my BT to the park and my friend brang his chocalate lab and wow, they were fine for like 5 minutes then they just went at it, of course my Bull terrier won with ease and really hurt my friend's dog but how do I prevent this from happening again

my only advice would be to not take your BT to any dog parks again. Only since it has dog-aggression issues and I wouldn't want to him to hurt another dog. Plus you could get him into trouble and be pts.
I can't move the thread, only the moderators can, but this should be in the "dog training" section.

I know it sucks, but you just gotta keep your's and other's dogs health in mind. Glad to hear that your friends dog is ok! And you should be glad it was a friends dog and not a strangers dog. You might of had a law suit on your hands!
Although, since I wasn't there I can't really give you advice on weither your dog was the aggresor or if your friends dog has some bad doggy manners.
Maybe if you can explain a little more of the events before the attack.
Like was your dog's legs stiff, where was the tail at? Was it wagging ? Slowly fast or medium? Any growling?
Just in as much detail as you can. Otherwise we can't help you as good.

Well you see my dog loves ball and I through it for him and my friends dog went and got it with my dog chasing him. Then they both jumped up on there hind legs and and started fighting. my dog was on top of my friends dog so we ran over and seperated them and my friends dog was bit just below the juggler vain in his neck.

So it could have been just object guarding! Have you tried letting your dog play with other dogs without any toys?
This is also one reason I don't bring my dogs to dog parks. There are a lot of fights over objects like balls and treats.